Polarimetric-radar signatures associated with the Greensburg, Kansas tornado

During the evening of 4 May 2007, a tornado devastated Greensburg, Kansas. A mobile, X-band, polarimetric, Doppler radar (UMass X-Pol), designed and built at the University of Massachusetts, and used by students at the University of Oklahoma, collected, at intervals of 1 – 1.5 min, volumetric, polarimetric, Doppler data in the parent storm for approximately 1.5 h, up until the time just before the storm hit Greensburg. The debris cloud from the tornado was best distinguished from the background of precipitation as a region of relatively low ρHV (cross correlation coefficient between the horizontally and vertically polarized signals). This debris signature was correlated with characteristics of the damage path as determined by personnel from the National Weather Service. In particular, documentation of the changing elliptical shape of the debris signature and the width and depth of the signature in relation to characteristics of the damage path are discussed. Implications of our findings for the detection of tornadoes and analysis of the nature of the debris cloud using polarimetric radars will be summarized.